Ductile iron pipes have often been used for plumbing. Such a ductile iron pipe is made by casting, and thus has a lot of flexibility in shape. Thus, there are a wide variety of joints, and each joint is used in a right place.
On the other hand, there are stainless steel (SUS) pipes for plumbing. However, it is not easy to process the joints for such SUS pipes. Thus, only SUS pipes with a specific diameter are used. Hereinafter, such a stainless steel pipe for plumbing will be referred to as an SUS tube. However, such SUS tubes have a useful life longer than ductile iron pipes. Furthermore, such an SUS tube reduces problems such as red or green rusty water and prevents stress corrosion cracking at room temperatures, and thus has a low running cost. Thus, there is a need for the use of SUS tubes of various diameters.
In order to connect SUS tubes, grooves are formed on the outer circumferences of the ends of two tubes to be connected, and a joint, which is to engage with the grooves, is attached to the tubes.
A form-rolling device is proposed as a device for forming such grooves. The form-rolling device includes: a drive transmitting mechanism embedded in a casing and including a rotation output unit; an electric motor that drives the drive transmitting mechanism; a driving roller attached along the inner surface of the tube and including a whole circumferential groove; a grooving roller pressed toward the driving roller while holding the tube between the grooving roller and the driving roller, and including a whole circumferential projecting part; a trajectory ring fixed on the tube and including a trajectory surface perpendicular to the axis of the tube; and a movable roller attached to the casing so as to be movable on the whole circumference of the tube along the trajectory surface (see Patent Literature 1).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2013-103237